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22nd Symposium on Fusion Technology (SOFT 2002), Helsinki, 2002-09-09 to 2002-09-13
Abstract:
The ASDEX upgrade vacuum vessel is equipped with 14 turbo molecular pumps (TMPs) and a
cryo pump (CP). The CP is cooled with boiling helium (He). To obtain similar conditions with the
CP for hydrogen (H₂) and deuterium (D₂) pumping a lower helium panel temperature (THP) is
required in the case of H₂. This is achieved by reducing the He boiling pressure (pb) and thus the He
boiling temperature (Tb) via pump down of the He cryostat. The requirements are predicted by
computations and verified experimentally for this case. By raising the cryostat pressure above
ambient, the prediction of the H₂ end pressure (peH₂) of the CP could be compared with
measurements in the range 5×10⁻⁷ < peH₂ (mbar) < 5×10⁻⁴. The beneficial effect of argon frosting for
helium pumping is only shown experimentally.
